There is an urgent need, worldwide, for improved contraceptives, especially prophylactic contraceptives. Barrier methods are the only class of contraceptives that protects users against sexually transmitted diseases. However, currently available spermicidal contraceptives suffer from poor efficacy and/or have undesirable toxicity. In a systematic effort to identify non-toxic spermicides potentially capable of performing better and without the drawbacks of detergent-type spermicides, we have rationally designed and synthesized several disubstituted metallocene derivatives. We discovered bis-cyclopentadienyl complexes of vanadium(IV) or vanadocenes to have rapid, potent, and selective spermicidal activity. Under Phase I funding, we demonstrated: (i) in vivo contraceptive activity of VDDTC via a gel-microemulsion in rabbits and porcine models; (ii) confirmed the lack of mucosal inflammatory potential of VDDTC in mice, rabbits, and pigs; (iii) developed a physiologically relevant and sensitive porcine model for vaginal irritation; and (iv) discovered that VDDTC significantly enhanced the microbicide efficacy of the antiretroviral spermicide WHI- 07 in the feline immunodeficiency virus/cat model of AIDS. Under SBIR Phase II support, we will expand the utility of the porcine and rabbit models to test the in vivo contraceptive efficacy, mucosal safety as well as developmental toxicity studies of VDDTC. We will perform these efficacy and safety studies of VDDTC in combination with WHI-07. We hypothesize that the combination of these two active agents with different mechanisms of action will potentially improve efficacy and duration of dual-protection when compared with VDDTC alone while maintaining an adequate safety profile. The goals of Phase II study are (i) to expand the utility of porcine model for the in vivo contraceptive efficacy of VDDTC versus VDDTC plus WHI-07 gel microemulsion; (ii) to expand the utility of porcine vaginal irritation model for the preclinical evaluation of VDDTC and VDDTC plus WHI-07 by characterizing the extracellular, cellular, molecular and histological endpoints; and (iii) to assess the developmental toxicity potential of VDDTC in rabbits. The proposed Phase II work will complement and enhance the discovery and preclinical development of safe and effective prophylactic contraceptives at Paradigm Pharmaceuticals that may provide the basis for a new strategy to prevent the sexual transmission of HIV while providing fertility control for women. [unreadable] [unreadable] [unreadable]